//响应头中间件
module.exports = async(ctx, next) => {
  const contentType = 'application/json; charset=utf-8';
  ctx.set('Content-Type', contentType);
  ctx.set("Access-Control-Allow-Origin", "*");
  ctx.set("Access-Control-Allow-Methods", "OPTIONS, GET, PUT, POST, DELETE");
  await next();
}